There is widely known a feedback control that brings an air-fuel ratio, which is a ratio between air and fuel in an exhaust gas exhausted from an internal-combustion engine, close to a target air-fuel ratio so as to improve fuel efficiency of a vehicle, and this air-fuel ratio is detected by an air-fuel-ratio sensor (A/F sensor).
As for an air-fuel-ratio sensor, there is known an air-fuel-ratio sensor that includes a gas sensor element in which a pump cell and a detection cell are provided and a controller controlling this gas sensor element. With regard to this air-fuel-ratio sensor, when an abnormality such as a short circuit between the pump cell and the detection cell occurs, reliable detection of an air fuel ratio becomes difficult. Therefore, there is proposed a technology that detects an occurrence of an abnormality of a short circuit between the pump cell and the detection cell (for example, Japanese Laid-open Patent Publication No. 2005-291991).
However, the aforementioned conventional technology has a fear that an abnormality of a short circuit between the pump cell and the detection cell is not detected with high accuracy.